Start by drying the raw chicken breasts with a paper towel, in order to soak up any extra moisture.
Cut the chicken into bite-sized cubes. You can do this by placing the chicken breast vertical to you, and cutting it in half length-wise. Then slice it in half length-wise again. Turn it horizontal to you and cut into 1-inch pieces.
Put the cubed chicken into a medium-sized bowl and season with salt and pepper.
Separate the egg whites of one egg into a small bowl and whisk with a fork until frothy—about 1 minute.
Pour the egg whites into the bowl of chicken, mix together, and place in the fridge with plastic wrap until ready to stir-fry.
To make the sauce, combine the soy sauce, hoisin, sesame oil, rice vinegar, honey and ground chili powder into a small bowl and mix well. Then mix in little amounts of cornstarch into the sauce until the whole 1 tbs. is used up. Then set it aside.
Next, cut the green beans in half or in thirds so that each green bean is 1-2 inches in length. Place in a bowl, rinse and then microwave for 1 minute to soften them just a little.
Next, heat a pan with ¼ cup oil on high. Cast iron pans or woks are great for cooking stir fries, as they conduct heat really well and keep the food hot. However, if you don’t have either of those pans, a frying pan works great too.
Using tongs, spread the chicken across the pan creating an even layer. Sauté the chicken until slightly undercooked, about 3-5 minutes. You want the chicken to be slightly undercooked before you add the vegetables, because you will need time to cook the vegetables, but don’t want to overcook the chicken.
Then add the green beans and mushrooms and sauté for 3-5 minutes.
Add the sauce and sauté for about 2 minutes or until the sauce thickens.
Serve with chopped scallions and a side of rice, and enjoy!